1. Field of Invention
This invention relates generally to a method for improving the dyeability of cellulose fabrics with reactive dyes by the treatment of the fabric prior to dyeing with an aqueous solution of oligomers of chitosan and stabilization by the subsequent treatment with sodium cyanoborohydride, sodium borohydride or other reducing agents. This new method enhances dye uptake, improves the texitle properties, and further reduces dyehouse polluting discharge.
2. Description of Related Technology
Reactive dyes are currently employed for dyeing cellulose fibers and show the greatest growth potential for use because of their wide shade range, ease of application, and excellent wet fastness properties.
There are, however, certain environmental problems related to the utilization of reactive dyes. These problems occur because high electrolyte concentrations must be used during the dyeing process. Additionally, the dyes have relatively poor uptake by the cellulosic fibers because between only 50-90% of the applied dye is covalently bonded to the substrate depending on application method, depth of shade and dye type used. As a consequence, the dyehouse effluents contain an unacceptable level of unfixed reactive dyes, electrolytes, and organohalogen residues which can cause environmental hazards and non-compliance with EPA discharge standards. Thus, a need exists for the treatment of cellulosic fibers to improve the reactive dyes uptake, to reduce the high concentration of electrolyte used in the dye bath, and to reduce the dyehouse toxic discharge without sacrificing the dyeability properties of the cellulosic fibers.
The ideal reactive dyeing process for cellulose fibers would be to exhaust the dye under neutral or slightly acidic conditions in the absence of electrolyte, and fixation of the dyes by raising the dye batch temperature to the boil or to approximately 100.degree. C. However, this process is impossible for the cellulosic fibers because of the existence of significant adverse charge barrier relationships between the negatively charged fibers and the negatively charged dyes in neutral or slightly acidic conditions. This charge barrier can be decreased or eliminated by adding large concentrations of electrolyte and/or by pretreatment of the cellulosic fibers by the introduction of primary amino, secondary amino, or tertiary amino groups to modify the fibers before dyeing with reactive dyes. The same effect can be achieved by the incorporation of fully quaternized cationic amino residues as the pretreatment step.
A number of patents and publications have considered the modification of cellulosic fibers with different classes of amides. Many low molecular weight compounds have been proposed for modification of cellulose. Rupin M., et al. (1970 Textilveredlung 5, 829). In Rupin M., et al. (1976 Textile Chemist and Colorist 8, (9) 139) N-(2-epoxypropyl)-trimethyl ammonium chloride commercialized by Protex, (Levallois, France) as Glytac A, was tested. Bayer, (Leverkusen, Germany) marketed another quaternized cationic amine, Levagen RS, which is glycidyl-N-methyl morpholinium chloride (Gipp, et al., German Offen. 2,407,147). These two quaternized amino products can react with cellulose under alkaline conditions.
Hartmann, U.S. Pat. No. 1,777,970 and from Margavio etal., (1965 American Dyestuff Reporter 54, (20) 71) discloses that 2-aminoethylsulfate can be introduced to the cellulosic fibers by thermal treatment in the presence of sodium hydroxide. Einsele-(1964, Milliand Textilberichte 45, 841) teaches that the resulting modified cellulose can be treated with monochloro-s-triazine reactive dyes. Good dye uptake and fixation was obtained in slightly acidic or neutral condition in the absence of electrolytes.
.beta.-chloroethyl-diethylamino hydrochloride has also been incorporated into cellulose under basic conditions. Soignet, D. M., et al. (1967 Journal of Applied Polymer Science 11, 1155). The resulting modified cellulose was tested by El Ally E. A., et al. (1986 American Dyestuff Reporter 76,(5) 22). Excellent affinity for reactive dyes was observed even for 2,4-difluoromonochlopyrimidine dyes. Lewis D. M., and Lei X. P. (1991 Journel of the Society of Dyes and Colourists (J.S.D.C.), 107, 191). Moreover, cellulose was treated with N-methylacrylamide and followed by ammonia, methylamine, dimethylamine, triethylamine and/or ethanolamine treatment. The resulting cellulose fibers could then be dyed with reactive dyes in the absence of electrolyte under neutral to slightly acidic conditions.
Other reactive quaterary compounds have been reported for treatment of cellulose to improve the reactive dyes affinity. Evans, G. E., et al. (1984 J.S.D.C, 100, 304); Kalk, W., et al, German Offen. 2,626,495; Perrin, P., et al., German Offen. 2,726,433; Stead, C. V., et al., U.K. Pat No. 2,119,367.
Polymeric compounds also have been used for cellulose treatment to improve the dyeability of fabrics. Courtaulds Co. and Sandoz Chemical Corp. (Basle, Switzerland) developed a cationic polymer pretreatment process (1989 Courtaulds Research Brochure Sandene Process). The resin, Sandene 8425, increased substantivity of cellulose for reactive anionic dyes and can be applied under neutral to weekly acidic conditions.
A reactive polyamide-epichlorohydrin resin (Hercosette 125 available from Hercules, Inc.) was studied for cellulose treatment of fabric by Burkinshaw S. M.,et al. (1989 J.S.D.C., 105, 391) with good results. Treated cellulose fibers could be dyed with highly reactive dyes without salt, or electrolytes from dye baths set at pH 7. Lewis D. M., et al. (1989 Text. Chem. Colorist 21, (10) 23) proposed the modification of this treatment which consists of an application of Hercosette or DMA-AC (1,1-dimethyl-3-hydroxyazetidinium chloride) in the presence of low molecular amine or thiol compounds.
Pretreatment, by the application of chitosan applied by the exhaust process to cover the immature (thin-walled) cotton fibers prior to dyeing with direct dyes has also been proposed. (Rippon J. A., 1984 J.S.D.C., 100, 298). Chitosan is a partially deacetylated poly (N-acetyl-D-glucosamine). This natural polymer is obtained from chitin by partial deacetylation in basic conditions. The application of chitosan by exhaust processing was investigated to improve the coverage of immature cotton fibers which were dyed with direct and reactive dyes. Mehta R. D. and Combs R. N. (Book, Pap.--Int. Conf. Exhib., AATCC, October 1-3, 1990, Boston, Mass., p. 214) Good results were obtained when the dyeing process was used with direct and reactant fixable Indosol dyes. This pretreatment was not as effective when using reactive dyes. However, in the case of reactive dyes, the chitosan treatment improved colour yields but caused increased stiffness of the fabric.
Thus, improvements have been sought to develop dye systems of increased substantivity under neutral or slightly acidic conditions which can decrease or possibly eliminate the amount of electrolytes required to be used during the dyeing process and to increase the efficiency of the dye to fiber covalent bonding reaction without sacrificing desirable textile properties.